1. Field of the Invention
The present invention relates to a silver halide emulsion having a high speed and enhanced gradation.
2. Description of the Related Art
With respect to silver halide photosensitive materials, silver halide tabular grains (hereinafter also referred to simply as “tabular grains”) have a multiplicity of advantages, so that they are now widely used in the field thereof. In recent years, the progress of related technology is striking. In the field of this technology, it is a well-known fact that the tabular grains have a large specific surface area and accordingly can increase the amount of sensitizing dye, capable of contributing to light absorption, adsorbed on silver halide grains, so that speed enhancement can be attained thereby. In this field, “speed enhancement” of tabular grains is an important theme. Speed enhancement technologies have been extensively and intensively studied in this field. Recently, for example, a method of sensitizing by the use of epitaxial junction has been disclosed as a technology for enhancing the speed of tabular grains (e.g., Jpn. Pat. Appln. KOKAI Publication No. (hereinafter referred to as JP-A-) 2001-235821). However, even the technology described in the patent application specifications is not satisfactory from the viewpoint of “speed enhancement”. Thus, there has been a strong demand for a new speed enhancement technology for tabular grains with a view toward developing a photosensitive material of further enhanced speed.
The present invention has realized such an enhanced speed as the prior art has failed to attain. In the prior technical literature including the above-mentioned patent publication, there is no description suggesting the subject matter of the present invention, namely, that a photographic performance of high speed and enhanced gradation can be achieved by an emulsion characterized by grains wherein a corner portion of each of the host tabular grains has epitaxial junction, wherein a region of an external surface of the epitaxial portion has a face parallel to the main plane of host grains and a region of the external surface of the epitaxial portion has a {100} face, and wherein the epitaxial portion has a dislocation line.